I have a 94 civic coupe. Most of my driving is city and for about 8 months the fastest sustained speed I was able to drive at was 50-60 mph. I got on the highway last week and was keeping up with traffic running above 70 for a few a few miles and when I pulled onto the exit ramp the car idled like crap and shut down. it started right back up but idled poorly and shut down on me another few miles down the road. It ran normal then a week passed and I went on the highway again and when I exited the idle dropped too low and I had to rev in order to prevent stall. any idea what is causing this? Too long creeping around at low speeds/rpms and maybe I blasted some deposits out of hiding when I opened up on the highway?